Stroke Rounds: Potassium Tied to Lower Stroke Risk

Action Points

An analysis of data from the Women's Health Initiative found that women who consumed the most potassium each day had a 12% lower overall risk of all stroke and a 16% lower risk of ischemic stroke when compared with women consuming very little potassium.

Note that among women without hypertension, those in the highest quartile of reported potassium consumption had a 27% lower risk of ischemic stroke than those in the lowest quartile.

A banana a day, or better yet some spinach or Swiss chard, just may keep the doctor away, if an association found in a new study proves to be causal.

An analysis of data from the Women's Health Initiative (WHI) found an inverse relationship between self-reported dietary potassium intake and stroke in postmenopausal women.

Women (mean age 63.6) who consumed the most potassium each day (>3,193.6 mg) had a 12% lower overall risk of all stroke (hazard ratio 0.88, 95% CI 0.79-0.98) and a 16% lower risk of ischemic stroke (HR 0.84, 95% CI 0.74-0.96) when compared with women consuming very little potassium (<1,925.5 mg/day), reported Sylvia Wassertheil-Smoller, PhD, of Albert Einstein College of Medicine in New York City, and colleagues.

In addition, among women without hypertension, those in the highest quartile of reported potassium consumption had a 27% lower risk of ischemic stroke than those in the lowest quartile, they wrote in the journal Stroke.

Women in the WHI cohort who did not have hypertension appeared to benefit the most from having higher amounts of potassium in their diets.

"Women with hypertension had a lower total mortality risk with higher potassium intake but no lowered risk of stroke, suggesting that higher potassium intake may be of more benefit before hypertension develops," the researchers wrote. "Healthcare providers, therefore, may wish to reinforce the importance of a potassium-rich diet especially among postmenopausal women."

Potassium and Stroke: Uncertain Link

Several other prospective studies have examined the potential impact of potassium on stroke risk, with somewhat mixed outcomes.

In a study reported almost 3 decades ago, women consuming <49 mmol (1,911 mg) of potassium daily had a relative risk of 4.8 (P=0.01) when compared with women eating >49 mmol of potassium. Another study reported in 1999 found that women in the highest quintile of daily potassium intake (median 3,555 mg) versus the lowest quintile (median 2,017 mg) had a relative stroke risk of 0.72 (95% CI 0.51–1.01).

And a 2011 analysis of the Swedish Mammography Cohort found that women with a history of hypertension had a relative risk of 0.64 for all stroke types when comparing highest quintile of potassium intake with lowest quintile (mean 3,834 mg daily versus 2,362 mg).

A meta-analysis that included 22 randomized controlled trials reported in BMJ in 2013 found higher potassium intake to be associated with a 24% lower risk of stroke, with moderate quality evidence.

But the European Prospective Investigation into Cancer and Nutrition-Netherlands (EPIC-NL) study, reported earlier this year, found no evidence that potassium intake was associated with stroke risk.

"Despite these useful contributions, it remains unclear whether higher dietary potassium intake is associated with reduced risk of all subtypes of stroke and whether these findings are especially relevant in specific population subgroups," Wassertheil-Smoller and colleagues wrote.

Study Details

The researchers evaluated data from 90,137 WHI enrollees between the ages of 50 and 79 who were followed for an average of 11 years. All women included the study were stroke-free at enrollment.

Mean reported dietary potassium intake was 2,611 mg/day. Black women, current smokers, and nondrinkers of alcohol reported lower dietary potassium intakes, and women who reported two or more recreational exercise sessions a week had greater dietary potassium intake than those who reported limited or no activity.

Stroke incidence per 1,000 person-years was 3.10 for all stroke types, 2.24 for ischemic stroke, 0.50 or hemorrhagic stroke, and 11.60 for all-cause mortality.

"Those in the lowest quartile of estimated dietary potassium intake (<1,925.5 mg potassium) had higher estimated (stroke) incidence than those in other quartiles across all outcomes," the researchers wrote. "There was a statistically significant linear trend for mortality (P=0.0002), but the linear trend did not reach statistical significance for the other outcomes."

When the researchers examined potassium intake by quartile and stroke risk, they found a statistically significant lower risk in all quartiles of potassium intake compared with the lowest intake quartile (<1,925.5 mg/d) for all-cause mortality, all stroke, and ischemic stroke in unadjusted multivariate models.

In the fully adjusted model comparing the highest quartile with the lowest quartile of potassium intake, the HR was 0.90 (95% CI 0.85-0.95) for all-cause mortality, 0.88 (95% CI 0.79-0.98) for all stroke, and 0.84 (95% CI 0.74-0.96) for ischemic stroke. No association with hemorrhagic stroke was seen.

In women without high blood pressure, there was a 27% lower risk of ischemic stroke in the highest quartile group compared with the lowest quartile group in the fully adjusted model (HR 0.73, 95% CI 0.60-0.88) and, again, no association with hemorrhagic stroke was seen. Higher potassium intake was associated with lower all-cause mortality in women with hypertension, but not lower stroke risk.

Cox analysis revealed that higher potassium intake was also associated with a lower risk of small-vessel disease among women who were not hypertensive. Compared with the the lowest quartile, HRs were 0.43 for quartile two, 0.60 for quartile three, and 0.67 for the highest quartile.

The suggestion from the findings that dietary potassium may be more beneficial before the development of hypertension supports cell culture and animal model studies showing that higher potassium levels improve vascular endothelial function and promote nitric oxide release to improve vascular flow, the researchers wrote.

Although higher potassium consumption has been linked to lower blood pressure in other studies, the correlation between systolic blood pressure and potassium intake was negligible in the WHI cohort study (-0.008), suggesting that "the beneficial effects of potassium intake among nonhypertensives was not modulated by its effect on blood pressure," they said.

"Our findings give women another reason to eat their fruits and vegetables," Wassertheil-Smoller noted in an accompanying press statement."

Red and white meat, many fish, and white beans are also good sources of potassium.

Study limitations included its observational nature, which precluded assumptions about causation. The estimates of potassium intake also came from food frequency questionnaires, which often overestimate or underestimate true intake, the researchers noted.

The study also relied on baseline dietary potassium to assess relationships with outcome and the researchers did not evaluate other potentially important dietary contributors to stroke risk.

They wrote that corresponding sodium consumption may be an important covariate in determining hypertension and cardiovascular risk, but sodium consumption was not reliably estimated in the WHI food frequency questionnaire.

Despite the limitations, the researchers concluded that higher potassium intake may protect postmenopausal women against ischemic stroke, death from all causes, and small vessel disease, especially if they do not have high blood pressure.

"Because dietary intake of potassium in the United States is well below the recommended intake, these findings are important in suggesting preventive dietary measures to lower the risk of stroke," they wrote.